Successful treatment of MAP2K1 mutant stage IV-M1d melanoma with trametinib plus low-dose dabrafenib: a case report

Clonal MAPK-pathway activating mutations in the MAP2K1 (MEK1) gene are present in approximately 9% of cutaneous melanomas. These mutations are divided into three classes: RAF-dependent, RAF-regulated, RAF-independent. Cell lines with class-2 or RAF-regulated MAP2K1-mutations are most responsive to MEK-inhibitors. We present a patient with a class-2 MAP2K1-mutant stage IV-M1d melanoma who experienced extra- and intracranial progressive disease following treatment with immune-checkpoint inhibitors. The patient was treated with the MEK-inhibitor trametinib (2 mg OD) to which a low-dose of dabrafenib (50 mg BID) was added to mitigate skin-toxicity. Following documentation of a partial response (PR), she developed one new, and increase in volume of two pre-existing brain metastases that were treated with stereotactic radiosurgery (SRS) while continuing trametinib and dabrafenib. Thereafter, a deep partial radiologic and metabolic response both extra-and intra-cranially was achieved and is ongoing 88 weeks after initiating trametinib. She experienced no grade > 2 adverse events. Focal post-radiation necrosis at site of an irradiated brain metastasis developed 9 months after SRS and is successfully being treated with low-dose bevacizumab. This is the first published case of a durable intracranial disease control with the MEK-inhibitor trametinib of a stage IV-M1d class-2 MAP2K1-mutant melanoma. This illustrates the utility of NGS profiles that include class-1/2 MAP2K1-mutations in patients with melanoma and other malignancies to provide valuable information on a potentially active individualized treatment option. A prospective clinical trial that further evaluates the efficacy of MEK-inhibitor therapies in MAP2K1-mutated tumors is justified.

MAP2K1, also known as MAPK/ERK-kinase-1 (MEK1), is a serine/threonine/tyrosine kinase that is activated by upstream RAF kinases.Clonal mutations in MAP2K1 are present in approximately 9% of cutaneous melanomas and activate the MAPK-pathway (4).
In this report, we present in more detail the case of a patient with a triple wild-type, class-2 MAP2K1-mutant AJCC stage IV-M1d melanoma, treated in the TraMel-WT trial, who had a deep and durable response to MEK-inhibitor treatment with excellent treatment tolerance (12).The patient provided written informed consent for publication.

Case description
A 40-year-old Caucasian female was diagnosed with a pT4bN1aM0 BRAF V600 wild-type cutaneous nodular melanoma on the left shoulder.During adjuvant pembrolizumab treatment, a solitary subcutaneous metastasis was resected and irradiated.One year after diagnosis, [18F]-fluorodeoxyglucose-positron emission tomography computed tomography ([ 18 F]FDG-PET/CT) revealed supra-and infradiaphragmatic lymph node and bone metastases.Treatment with ipilimumab/nivolumab was initiated.She developed immune-related colitis after two cycles and progressed with seven new brain metastases (AJCC stage IV-1Md) (Figure 1A).Comprehensive genomic profiling through next generation sequencing (NGS) revealed a clonal class-2 RAF-regulated MAP2K1 mutation (Q58_E62del, allele frequency 37%, in-frame-deletion; the complete NGS results can be found in Table 1).The patient initiated trametinib 2 mg once and dabrafenib 50 mg twice daily in the TraMel-WT trial in September 2022.Low-dose dabrafenib was associated upfront to mitigate skin-toxicity (12,13).She did not receive any local intracranial therapy at this time for the brain metastases.After 5 weeks, brain MRI revealed no new lesions and baseline lesions were considered stable according to RANO-BM criteria (14).Response assessment in week 7 with [ 18 F] FDG-PET/CT showed complete metabolic response of extracranial lesions (Figure 1B).After 14 weeks of treatment, brain MRI indicated complete regression of five brain metastases.However, there was one new lesion (6 mm longest diameter) and an increased diameter of two preexisting metastases (Figure 1C).At the patient's request, close surveillance rather than immediate radiotherapy was applied while continuing trametinib and dabrafenib.Following confirmed progression in these three lesions nearly 2 months later, they were treated with stereotactic radiosurgery (1 × 20 Gy) (Figure 1D).A follow-up MRI (week 32) showed decrease in all three lesions and no new lesions.After 66 weeks of treatment, the patient remained in complete metabolic remission extracranially (Figure 1E).The week-59 brain MRI confirmed a continuing decrease in diameter of one of the irradiated lesions, and complete regression of the others (Figure 1E).
Treatment was well tolerated.She intermittently reported low-grade nausea, pruritus, epigastric pain and fatigue, but did not experience skin-toxicity.No dose reductions of trametinib or dabrafenib were required.
While extra-and intracranial responses persisted, the week-59 brain MRI revealed signs of focal post-radiation necrosis of the brain (fRNB) approximately 8 months after SRS for the lesion in the paramedian frontal right region (Figure 2A).A brain MRI, repeated 6 weeks later, showed increase in contrast-enhancement and size of the region (Figure 2B), which was associated with headaches.In order to differentiate between fRNB and tumor progression, an [ 18 F]FDG-PET/ CT of the brain was performed and demonstrated focal hypometabolism at the region of the gadolinium-contrastenhancement, supporting the diagnosis of fRNB.A low-dose bevacizumab treatment regimen (previously established as effective treatment for fRNB) was initiated to treat the perilesional edema (15) (Figure 2C).After two doses of bevacizumab (8 weeks) the headache subsided and MRI showed an important decrease in contrastenhancement and edema (Figure 2D).
At the moment of writing, after 88 weeks of treatment, the patient continues to have a radiological response and remains on treatment (trametinib with low-dose dabrafenib and bevacizumab), while maintaining an active lifestyle.

Discussion
No approved therapies have shown to improve OS in patients with BRAF V600 wild-type melanoma who progress on ICB.In melanoma with non-NRAS Q61 /BRAF V600 , MAPK-pathway activating mutations, MEK-inhibitor therapy has shown anti-tumor activity (12,16,17).In vitro trametinib has activity in triple wild-type melanoma cell lines (18).In MAP2K1-mutant melanoma, there is one case report of a partial response to trametinib in a patient with stage IV-M1c melanoma, but resistance developed 3 months later and dose reduction was needed because of trametinib-induced skin-toxicity (Table 2) (19).To the best of our knowledge, this is the first case report of stage IV-M1d MAP2K1-mutant melanoma with a durable extracranial complete response and intracranial disease control with trametinib and low-dose dabrafenib.Our patient initially had unconfirmed PR, thereafter oligo-progression in the brain, which was managed locally with SRS while continuing trametinib and dabrafenib.Eventually, a deep and durable disease control, both extra-and intracranially, was achieved.
The prognosis and natural evolution of AJCC stage IV-M1d, BRAF-wild-type melanoma with active brain metastasis progressing on ICB is very poor.In this patient, the brain metastases were successfully controlled: the majority disappeared with trametinib and no new lesions emerged following SRS, maintaining disease control for more than 20 months at moment of writing.
MAP2K1 mutations can be classified into three groups.Class-1, RAF-dependent MAP2K1-mutations are dependent on upstream RAF-activation to induce high levels of activated phosphorylated ERK (pERK), likewise the pathway is self-limited by feedback inhibition of RAS or RAF.Class-2, RAF-regulated MAP2K1-mutations are partially     Frontiers in Medicine amounts of RAF-independent activity.Finally, class-3, RAF-independent mutations induce high levels of pERK without upstream RAF-activation and are not susceptible to feedback inhibition (11).Class-1/2 MAP2K1-mutations are usually associated with upstream mutations in RAS, RAF, or NF1, while class-3 MAP2K1-mutations do not coexist with other mutations.MAP2K1-mutations have been successfully targeted in vitro with MEK-inhibitors that preferably bind to the inactive, unphosphorylated form of the MEK1-enzyme.Both class-1 and -2 MAP2K1-mutations are (partially) RAF-dependent, suggesting a significant inactive fraction of the mutant MEK1enzymes and thus sensitivity to trametinib.Class-3 mutated proteins on the other hand are resistant to allosteric MEK-inhibitors due to their permanently active conformation (11).The MAP2K1-mutation (Q58-E62del) found in our patient, results in an in-frame deletion and is classified as class-2 RAF-regulated MAP2K1-mutation (28).In accordance with these preclinical results, the melanoma lesions in our case responded to trametinib.
A recent retrospective review of the AACR genie, a clinicogenomic database showed that co-occurring MAPK-pathway mutations (e.g., NRAS, NF1) are significantly more likely with class-1 MAP2K1-mutations (82.3%) compared to class-2 (30.9%) and class-3 (10.6%) in any tumor type.This highlights that additional activation of the MAPK-pathway is needed to induce malignant cell growth in class-1 RAF-dependent MAP2K1-mutant tumors, that this is to a lesser extent necessary in class-2 MAP2K1-mutant and not necessary in class-3 MAP2K1-mutant tumors.Class-2/3 MAP2K1-mutations can therefore act as a driver mutation.Additionally, patients receiving MAPK-inhibitors, with class-2 MAP2K1-mutations derived the most benefit, translating to a longer PFS (4.0 months) and duration of response (23.8 months) (29).
Several other cases of successful MEK-inhibitor use in MAP2K1mutant malignancies have been documented, primarily non-Langerhans cell histiocytosis and hairy cell leukemia (Table 2) (30).Responses were observed in cases with class-2 and -3 MAP2K1mutations, however in the class-3 cases, responses were mostly shortlived.These data show the importance of precision oncology and systematic genomic analysis through NGS in both triple wild-type melanoma and other malignancies in which no classical driver mutations have been identified to expand possible treatment options.
Another point of interest is that in five of the seven cases reporting adverse events, rash or acneiform dermatitis were reported (Table 2).In one case this led to treatment discontinuation, in another trametinib dosing was reduced (19,25).In our patient trametinib-induced skintoxicity was successfully prevented by adding low-dose BRAFinhibitor, as previously reported by our group, seemingly without compromising MEK-inhibitor activity (12,13).Consequently, the patient has an excellent and durable tolerance of full dose trametinib.
Of note, the patient developed fRNB 8 months after SRS, a late side effect of SRS with increasing frequency as more effective therapy Frontiers in Medicine helps distinguish fRNB from tumor progression, with fRNB showing decreased [ 18 F]FDG uptake (hypometabolism) and tumor progression showing increased uptake (hypermetabolism) (15,31).Our group recently reported a case series of successful fRNB treatment using low-dose bevacizumab (loading dose of 400 mg, followed by 100 mg q4w) (15).This regimen was effective and well tolerated alongside trametinib and dabrafenib in our patient.

Conclusion
We report the first case of durable intra-and extracranial response to trametinib, following local control with SRS of intracranial oligoprogression, in a patient with stage IV-M1d class-2 MAP2K1-mutant melanoma.Association of low-dose BRAF-inhibitor prevented MEK-inhibitor-induced skin-toxicity.Precision oncology using NGS data to screen for MAP2K1-mutations offers valuable treatment insights.A cross-tumor prospective trial is needed to evaluate the efficacy of MEK-inhibitors in MAP2K1-mutated tumors.

FIGURE 1
FIGURE 1 Case presentation with radiological evaluation with [ 18 F]FDG-PET/CT (maximum intensity projections and fused axial images) and contrast-enhanced T1-weighted MRI of the brain.(A) Baseline, week minus 3 shows hypermetabolic supra-and infradiaphragmatic lesions on PET/CT.In the brain, a lesion can be noted parafalcine in the left (L) occipital lobe (4 mm; upper image) and no lesion is noted in the right (R) nucleus caudatus (lower image).(B) PET/CT in week 7 shows a significant decrease in metabolic activity as well as a decrease in size of the lesions (unconfirmed partial response).Brain MRI at week 5 shows a slight increase of the L occipital parafalcine lesion (7 mm, upper image), however there are no new lesions and considering a lead time bias of 3 weeks the treatment is continued.(C) On brain MRI in week 14, the parafalcine L occipital lesion has disappeared (upper image), a new lesion in the nucleus caudatus has emerged (lower image).(D) PET/CT in week 24 shows a metabolic remission extracranially.MRI shows an increased size of the lesion on the nucleus caudatus (lower image); SRS is performed for this lesion and 2 other progressive lesions (not shown).(E) PET-CT in week 66 shows a sustained complete metabolic remission, MRI in week 59 shows a shrinkage of the lesion in the caudatus (lower image), no other intracranial lesions are detectable on MRI.BID, twice a day; dab, dabrafenib; OD, once daily; SRS, stereotactic radiosurgery; trame, trametinib.

FIGURE 2
FIGURE 2 Case presentation of focal post-radiation necrosis of the brain (fRNB) with gadolinium contrast-enhanced T1-weighted and FLAIR MRI of the brain and [ 18 F]FDG-PET/CT (FDG-uptake images).(A) First sign of fRNB (week 59 or 32 weeks after SRS) with contrast-enhancement in the paramedian frontal right region on the T1-weighted axial image (upper) and surrounding edema on the FLAIR axial image (lower).(B) In week 65 or 38 weeks after SRS there is an increase of contrast-enhancement in the paramedian frontal right region on the T1-weighted axial image (upper) and surrounding edema on the FLAIR axial image (lower).(C) PET-CT performed 1 week later (week 66 or 39 weeks after SRS) shows no increased uptake of [18F]FDG, supporting the diagnosis of fRNB.(D) In week 74 or 8 weeks after bevacizumab initiation there is a decrease of contrast-enhancement in the paramedian frontal right region on the T1-weighted axial image (upper) and surrounding edema on the FLAIR axial image (lower).SRS, stereotactic radiosurgery.

TABLE 1
Comprehensive genomic profiling of the presented patient.
1These mutations are reported as being likely pathogenic following the comprehensive genomic profiling.VAF, variant allele frequency; VUS, variant of uncertain significance.

TABLE 2
Overview of case reports describing patients with an MAP2K1-mutation treated with trametinib.